Congenital mesenchymoma of tibia: case report and review of literature.

Fibrocartilaginous mesenchymoma is a rare bone tumor arising from long bones in children and adolescents. With only 21 cases reported in the literature, it is often not included in the differential diagnosis in patients with a bone tumor. Previously, the youngest case reported was in a 19-month-old boy, and a congenital variant had not been reported. We describe a case of congenital fibrocartilaginous mesenchymoma of the proximal tibia that presented shortly after birth. Biopsy of a suspected malignancy on imaging confirmed the diagnosis. The child was temporarily lost to follow up and presented again with genu varum and limb shortening but surprisingly, the tumor had completely resolved without surgical intervention.